Sink basin



FIG. 1 is a top view of a sink basin; and,

FIG. 2 is a top perspective view of a sink basin.

The broken line showing of the environment is for illustrative purposes only and forms no part of the claimed design. The boundaries of the claimed design shown in broken lines form no part of the claimed design. 

I claim the ornamental design for a sink basin, as shown and described in FIG.
 1. 